Technical Abstract:
Salmonella Enteritidis contaminates the contents of the hen egg and it is thus a major world-wide food safety problem. High-molecular-mass LPS (HMM LPS) produced by some isolates alters avian reproductive tract biology. Cooperation between orally invasive and parenterally-adapted subpopulations appears to be required to achieve high-incidence egg contamination. Objectives were to determine if parenterally adapted subpopulations that make HMM LPS and have reproductive tract tropism emerge during the infection pathway to the egg. Methods: Neutral sugar compositional data were derived by gas chromatography of derivatized LPS obtained from isolates cultured from experimentally infected hens, from the spleens of naturally infected mice, and from United Kingdom isolates. Statistical analyses were performed as indicated. Results: The probabilities that avian isolates produced HMM LPS suggested that U.S. mouse isolates were most like U.S. avian intestinal samples, whereas UK isolates were most like avian reproductive tract and egg isolates. Non-reproductive tract organ isolates had significant loss of O-chain. Isogenic isolates with different abilities to make biofilm and to be orally invasive produced different O-chain structures at 25 but not at 37 degrees C. Hens infected at a 91:9 positive/negative biofilm colony phenotype ratio yielded only the negative phenotype from eggs. Conclusions: These results indicate that the hen applies stringent selection pressure to subpopulations of Salmonella Enteritidis. The avian cecum was an early environment that supported emergence of strains producing HMM LPS. These results suggest that diet and other factors that alter gut physiology could be manipulated to specifically reduce egg contamination as compared to just achieving reduction in intestinal colonization.